Various elevators for use in emergency situations have previously been described. For example, U.S. Pat. No. 927,056 to Krasmer describes a fire escape elevator type device wherein the cage rides on rotating worms, the cage being raised by a spring motor which is wound upon descent of the cage. The cage is stopped at any particular level by outwardly protruding arms which contact the top of the cage. No means are apparently provided to control the rate of ascent or descent of the cage which would vary depending upon the load. U.S. Pat. No. 815,401 to Breckon discloses a fire escape elevator type device wherein the elevator is raised by counterweights running in vertically disposed guides. The cage is slowed in its vertical descent by a brake disposed at the top of the elevator mechanism, the controlling cable for the brake running through the cage. This particular device does not suffer from the same relative degree of mechanical complexity as the device disclosed by the patent to Krasmer, although it is still relatively mechanical complex particularly in relation to the pulley mechanism for engaging the brake activating cable. It is desirable to keep such devices which are particularly intended for emergency situations, as mechanically simple as possible in order to minimize the possibility of failure of the system as a result of a failure in one of its mechanical components. The device described in the patent to Breckon in addition to being subject to possible failure of the mechanism for engaging the brakes, is also subject to possible failure of the brake itself, the failure to the brake most likely resulting from overheating.
U.S. Pat. No. 494,217 to Miles describes a pneumatic elevator having a cage connected through a cable and pulley to a piston disposed in a vertically oriented cylinder. The cylinder has relief valves connected to either end, the valve connected to the upper end being capable of allowing air to exit from the upper end of the cylinder upon descent of the elevator, or allowing compressed air from a source of compressed air to enter the upper end of the cylinder in order to raise the cage. Such a device suffers not only from the possibility of failure in the relatively complex valve mechanism required for communication with the upper end of the cylinder, but also from possible failure of the source of compressed air, the source of compressed air described in the patent being a compressor run by a steam powered engine. Obviously, other sources of power could be used to run the compressor. If however, the source of steam or electricity or otherwise should fail during an emergency, the cage of the elevator could not be raised. Furthermore, during emergency situations such as a severe fire, the source of power for the compressor could readily be interrupted.
U.S. Pat. No. 780,711 to Donnell describes a fire escape elevator type device with a relatively complex cage structure designed to rescue occupants of a building from windows of the building adjacent either side of the path of travel of the cage. The device relies upon the strength of individuals located on the ground to control the speed of descent of the cage and also to raise it. The device would require at least two people on the ground and probably three for proper operation. Obviously, it is undesirable to have to rely upon the presence and strength of individuals located on the ground during an emergency situation.
U.S. Pat. No. 407,200 to Guthrie describes an emergency fire escape elevator device wherein the cage is raised by counterweights disposed in vertically oriented tubes, and is controlled in its vertical descent by brakes, the control ropes for which extend through the cage. Pistons are rigidly attached to the cage so as to move up and down within a corresponding direction. These pistons move into corresponding cylinders with an open upper end, the lower end of which is closed and communicates with a valve for gradually releasing air. As a result, the cage is gradually slowed in its descent even if the brake should fail (which as mentioned before can readily happen in heat producing devices such as brakes). The device described by this patent is relatively complex to manufacture, requiring at least one counterweight and a separate guide tube, as well as at least one piston and its corresponding open ended cylinder and also a brake. As well, this particular device does not control the speed of descent of the cage throughout its entire descent, nor does it control the speed of ascent of the cage.
It is desirable then to have an emergency elevator device which is relatively simple to construct so as to have few parts which can malfunction, and which does not depend upon any source of power, including human power. As well, it is desirable to have such a device which has no heat producing components, such as brakes, which may malfunction during an emergency as a result of overheating.